In a liquid crystal display (LCD), the orientation direction of a liquid crystal is controlled with an alignment layer disposed on a substrate. The alignment layer is formed in such a manner that a thin-film made of polyimide or an inorganic material is irradiated with ion beams such that the bonds between atoms in the thin-film are broken. If the surface of the thin-film is subjected to alignment processing, that is, alignment treatment, effective in aligning the liquid crystal by ion beam irradiation, the distribution of the irradiation direction of the ion beams corresponds to that of the orientation direction of the liquid crystal. Hence, it is preferable that the spread of the ion beams be small and the ion beams be aligned in a predetermined direction.
According to a conventional technique, as shown in FIGS. 1(a) and 1(b), ion beams 28 are applied to a thin-film 26 while a substrate 24 is being moved close to or away from an ion source 12. Since the ion beams 28 spread as described below, a mask (a shielding plate) 20 is used to apply only some of the ion beams 28 that are useful in forming an alignment layer to the thin-film 26 through a slit 22. In order to subject the entire surface of the thin-film to alignment treatment uniformly, it is ideal that ions are applied to the thin-film 26 in such a manner that the ions form parallel beams with uniform ion density.
The orientation direction of a liquid crystal needs to be uniform over the alignment layer. The misorientation of the liquid crystal causes brightness or color non-uniformity in liquid crystal panels. Therefore, in order to manufacture a high-image-quality liquid crystal panel, the liquid crystal needs to be more uniformly oriented.
In order to uniformly orient the liquid crystal, the ion beams emitted from the ion source need to have uniform density. The density of the ion beams is rendered uniform by controlling the density of gas in a plasma-generating chamber and the density of generated free electrons.
As shown in FIG. 1, the ion source for generating the ion beams 28 usually includes a plurality of sheet-shaped grids 11. Each grid 11 has a plurality of outlets for emitting the ions. The ion beams 28 emitted through the outlets spread. In order to allow the ion beams to have uniform intensity or density distribution, the outlets have different sizes depending on the ion density in the ion source as disclosed in U.S. Pat. No. 6,849,858.
If a region extending in the X direction in FIG. 1B, that is, in the direction perpendicular to the traveling direction of the substrate, is irradiate with the ion beams with different intensities, misorientation occurs in the thin-film 26 subjected to alignment treatment.
U.S. Pat. No. 7,057,692 discloses that the ion beams 28 are aligned in one direction in such a manner that the shape of an edge 32a of the mask 20 that defines the slit 22 is varied or corrected depending on the orientation direction of the liquid crystal.
The above conventional techniques have the following problems: a problem that an apparatus needs to be precisely manufactured, for example, the grid needs to be precisely machined such that the ion beams emitted from the ion source have uniform density and/or the mask edge needs to be precisely shaped such that the ion beams are aligned in one direction and a problem that the process time required to apply the ion beams to the irradiation region becomes long because the irradiation region is narrow.